Ink jet printers are a well known and widely used form of printed media production. Colorants, usually ink, are fed to an array of micro-processor controlled nozzles on a printhead. As the print head passes over the media, colorant is ejected from the array of nozzles to produce the printing on the media substrate.
Printer performance depends on factors such as operating cost, print quality, operating speed and ease of use. The mass, frequency and velocity of individual ink drops ejected from the nozzles will affect these performance parameters.
Recently, the array of nozzles has been formed using microelectromechanical systems (MEMS) technology, which have mechanical structures with sub-micron thicknesses. This allows the production of printheads that can rapidly eject ink droplets sized in the picolitre (×10−12 litre) range.
While the microscopic structures of these printheads can provide high speeds and good print quality at relatively low costs, their size makes the nozzles extremely fragile and vulnerable to damage from the slightest contact with fingers, dust or the media substrate. This can make the printheads impractical for many applications where a certain level of robustness is necessary. Furthermore, a damaged nozzle may fail to eject the colorant being fed to it. As colorant builds up and beads on the exterior of the nozzle, the ejection of colorant from surrounding nozzles may be affected and/or the damaged nozzle will simply leak colorant onto the printed substrate. Both situations are detrimental to print quality.
To address this, an apertured guard may be fitted over the nozzles to shield them against damaging contact. Ink ejected from the nozzles passes through the apertures on to the paper or other substrate to be printed. However, to effectively protect the nozzles the apertures need to be as small as possible to maximize the restriction against the ingress of foreign matter while still allowing the passage of the ink droplets. Ideally, each nozzle would eject ink through its own individual aperture in the guard.
As the apertures in the guard are generally microscopic they can be easily clogged. Therefore, it is often desirable to keep the exterior of the nozzle guard clean especially in environments with relatively high levels of dust and other airborne particulates. This is conveniently achieved using a wiper blade that periodically sweeps across the exterior face of the guard to remove dust or ink residues. However, the residual matter on the wiper often becomes lodged on the exterior rim especially the portion of the rim facing into the wipers' direction of travel. This build up of residue tends not to get removed by the wiper and can soon clog the aperture.
To overcome this, the exterior surface can have recesses around each of the apertures so that the wiper blade passes over without engaging the aperture rim. However, the recesses around each of the apertures require the spacing between adjacent apertures to increase. This in turn lowers the nozzle packing density on the printhead and thereby increases the printhead manufacturing costs.